Electron discharge device



May 9, 1939. M. E. MACKSOUD ELECTRON DISCHARGE DEVICE Filed April 28, 1957 2 Sheets-Sheet l May 9, 1939. M E. M-ACKSOUD ELECTRON-DISCHARGE DEVICE 2 Sheets-Sheet 2 Filed April 28,, 1937 Patented May 9, 1939 UNITED STATES;

2,157,552 ELECTRON mscrmacn mzvron Michel E. Macksoud, St. Albans, N.

to Macksoud Patents, Inc., corporation of New York Y., assignor New York, N. Y., a

Application April 28, 1937, Serial No. 139,418

13 Claims. (01. 176-122) This invention relates to electron discharge devices, and consists in an aut ically regulating electron discharge tube desigi d to eliminate the need for external current limiting means such as the usual transformers, resistances, reactances, rheostats, etc., and to provide in a single and unitary structure a complete self-sufiicient, automatically regulating tube. My invention also includes within its scope the novel method herein disclosed of regulating current flow through an electron discharge tube by means of a variable electron barrier.

The essential feature of the device of my invention is a free or isolated electrode so constructed and arranged as to impede the electron flow between the cathode and anode of the device to the extent of forming a variable barrier and to balance the rate of replenishment of electrons intercepted thereon against the rate of current flow through the device.

The field of application for the tube of my invention is wide and is particularly adapted for illumination. Other important fields are in the amplification, regulation and control of current devices such as that made possible by tubes of the Thyratron class. Further important fields are in the amplification of high or low frequencies such as those employed in radio appliances, sound motion pictures, telephone repeaters and numerous applications in the field of conununication or entertainment.

Before discussing the mechanical construction of my automatic regulating tube it-will be desirable briefly to review the theory upon which such electron discharge devices operate. It will be understood that if any given potential is created between an anode and cathode there will be a voltage distribution in the intervening space depending to a large extent on the configuration of the electrodes. If the electrodes are considered as fiat plates the voltage distribution will be uniform between them. As the electrons travel from the cathode to the anode they move continually into the regions of higher voltage. Consequently at any point in the space which is at some degree a higher potential than the zero potential of the cathode, it may be said that an electrode has at that point fallen through a certain voltage the value of which is given by the voltage-distribution curve for the given electrode shape. The electron, when released from the cathode is caused to travel toward the anode at an accelerating rate because of the applied voltage and thereby it gains kinetic energy. If the electron starts from the cathode with zero speed it will at any point in space have a speed which depends only on the voltage at that point. With respect to a vacuum tube this relation makes possible the statement that the electric current passing through the tube depends upon the number of electrons that travel past any point in the tube each second. Since the current through the tube depends on the velocity of the electrons which in turn depends upon the impressed voltage, intensity of current flow also depends on the voltage distribution in the space between the cathode and the anode.

For a current of even a few milli-amperes, an enormous number of electrons is required so that there is a cloud of electrons which is dense near the cathode and which thins out toward the anode. It is this cloud of electrons which constitutes the space charge; and the lowering of the voltage in the space occupied by the cloud of electrons is known as the space charge effect. Therefore, the number of electrons reaching the anode or the electric current flowing through the tube depends on the voltage distribution between the anode and the cathode when that space is occupied by electrons.

If a sufiicient number of gas molecules are left in the space between the electrodes, it is very probable that some of them will become ionized by electron impact. These ions have a positive charge, and because their mass is large they remain in the space a long time compared to the electrons. These positive charges neutralize some of the efiect of the negative charges of the electrons and raise the space potential, thus permitting more electron current to flow. A relatively small numberof ions can neutralize so much of the space charge that the foregoing rule will not hold. If enough ions are present, the discharge may become so great as to destroy the tube by overheating the anode. This will result in a continuously increasing current and due to the negligible voltage drop, will cause serious burnout of the tube or circuits. x

It is for this regulation of the current flow, so that it may be controlled at any given or predetermined value without the requirement of external circuit means, that the isolated free electrode placed at some point in this electron path may be utilized to great advantage.

If an isolated free electrode be placed at some point in the space between the anode and the cathode, this free electrode will, in the presence of an electron flow, assume the potential of that given point. The potential of this free electrode which is positive with respect to the cathode will hence attract the electrons which are by their nature negatively charged. A large quantity of the electrons liberated from the cathode will continue to flow to the anode, while a certain portion of the electrons will adhere to the positively charged free electrode. The current flow between cathode and anode will be determined by the electron flow between them. However, as the current intensity increases, more and more electrons continue to build up an electron barrier on the free electrode in that their accumulative negative charge reduces the positive charge of the free electrode and this in turn causes a decrease in the intensity of the electron stream.

There are several forms that this free electrode may take, the most preferable being a mesh structure. This may be shaped as a cylindrical sleeve with a definite number and size of apertures in it. As this electron barrier is built up it tends to act like a dam to further electron and current flow. As the value of the current intensity decreases correspondingly with the decrease in intensity of the electron flow from cathode to anode and through the free electrode, the free electrode becomes less positive in its potential due to bombardment by the negative electrons. As this occurs, the attractive force that holds the electrons to the free electrode drops sufliciently to permit a portion of these barrier electrons toleak oil into the voltage distribution space. This causes the positive charge of the free electrode to again increase and this in turn causes an increase in the electron flow to the anode. The process of building up and leaking off of electrons on the free electrode remains constant with respect to the size of the mesh openings of the'free electrode. Consequently, a limited and predetermined maximum current flow will be maintained between cathode and anode, without any external means for its regulation. One or more of these free electrodes may be employed in the electron path, as well as one or more cathodes, in the various devices in which this principle may be employed.

By this method, the electrode design and structure, and the application of electron phenomena occurring on a free electrode located in the voltage distribution space, we derive a. new principle, that permits the automatic functioning of an electrode that is totally isolated from any circuit connection to act in such a manner that with increase of current flow between cathode and anode, the free electrode increases its resistance to the electron flow and current discharge. In a simple electrode we therefore have an automatic current limiting means that is a component part of the tube structure.

This principle may be utilized in the design of a gaseous discharge lamp similar in size and shape to an ordinary incandescent filament lamp, and which may be connected in any available service circuit without external energization current limiting means. It has been appreciated that a greater quantity of lumens per watt is obtainable from this type of gaseous discharge lamp, although such lamps have heretofore required transformers for their operation and are necessarily bulky.

In a gas filled tube the gas discharge is made up of three types of particles; the electrons, the neutral gas atoms and the positive ions. Each of these three constituents has its own characteristics and each plays an important role in the conduction of current from cathode to anode. In a high vacuum tube the electrons follow a continuous path from the cathode to the anode,

but in a gas filled tube the movement of the electrons is interrupted by collisions with gas atoms and these collisions result in the formation of positive ions and free electrons.

These positive ions raise the space potential and permit more electrons to leave the cathode. If the rate of ion generation ,is great enough, some point in the space may become more positive than is normal at that point. Electrons flow into the area of such a point and lower the potential by adding negative charges, until the number flowing in just balances the number which can escape through the small retarding potential to the anode. This high potential area, therefore, acts like a trap for the low-speed electrons.

The characteristics of the different regions of the space between the cathode and anode of a gas filled lamp are quite different and have been given distinguishing names. The regions of large potential change are called sheathes and the region where the change in voltage is slight and the number of ions is nearly the same as the number of electrons is-called the plasma. The sheathes may cover every part of the tube including the walls and all insulating elements. There is no preponderance of charge of one kind arriving on the insulating parts of the tube because practically no current can flow from them. Consequently the positive ions and negative electrons arrive in equal numbers. The insulating elements, such as the glass walls, therefore acquire a potential negative with respect to the plasma.

If a fine screen mesh is used for the free electrode member, the current density between anode and cathode will depend upon the size and thickness of the openings in this mesh, as well as the factors of voltage difference between cathode and anode, and their geometrical size and spacing. However, I am concerned primarily, with the size and thickness of the interstices of the mesh, as these factors determine the relation of current flow to the resistance of the free electrode, as already explained.

It will be understood that the free electrode functions automatically to limit the current flow in a gas or vapor-filled tube and maintain it steadily at a predetermined and fixed maximum value. The free electrode therefore permits the current load to build up to maximum, and when this fixed value of current density is reached, this free electrode functions in a manner to limit and prevent further increase in the load.

The novel features and characteristics of my invention will be best understood and appreciated from the following description of several preferred embodiments thereof selected for the purposes of illustration and shown in the accompanying drawings in which,

Fig. l is a view in elevation, partly in longitudinal section, of a tube for illuminating purposes,

Fig. 2 is a cross sectional view of one electrode un t,

Fig. 3 is a fragmentary view in perspective of the same unit,

Fig. 4 is a circuit diagram of the tube of Fig. 1,

Fig. 5 is a view in elevation, partly in longitudinal section, of a tube having electrode units of somewhat different arrangement from. those of the tube of Fig. l,

Fig. 6 isa fragmentary view in perspective of one of the units of the tube of Fig. 5,

Fig. 7 is a circuit diagram of that tube,

Fig. 8 is a view in elevation, partly. in longitudinal section, of a tube having a single electrode unit,

Fig. 9 is a view of the unit in cross section,

Fig. 10 is a fragmentary view in perspective of the unit of Fig. 8,

Fig. 11 is a circuit diagram of the tube ,of Fig. 8,

Fig. 12 is a view in elevation, partly in longitudinal section, of a tube having a single electrode of somewhat different construction from that of Fig. 8,

Fig. 13 is a fragmentary view in perspective of the electrode of Fig. 12 and Fig. 14 is a circuit diagram of the tube of Fig. 12. v

The tube shown in Fig. 1 comprises a bulb H) which may be of conventional shape having a threaded metallic base H and a. stem or mount l2 in which is sealed a pair of lead wires l3 and I4, preferably braided and adapted to carry a relatively heavy current. The bulb as herein shown is provided with a reflecting coating l of metallic silver which extends from the line of maximum bulb diameter to a line in the neck of the bulb. The purpose of this coating is to direct and concentrate all the light from the glow discharge light source into a single well defined beam or field.

The bulb contains two electrode units herein shown as supported at the upper ends of the glass tubes 16 which also serve as insulators for the lead wires. Each of the electrode units comprises a core of lava or other refractory substance comprising a base flange l7, an elongated tubular sleeve or body I 8 and an upper flange l9. Both flanges are centrally perforated to receive a coiled heater wire 20 of nickel or tungsten. these being connected at their upper ends by a transverse connecting wire 2|. The resistance of the heater wire is sufficiently high to perm t it to be directly connected in the service circuit without supplementary resistance of any kind. While I prefer to use refractory metal for the heater, a carbon filament or rod would serve as well if desired. The primary purpose of the heater wires 20 is to heat the cathode and stimulate its rate of electron emission.

One electrode of each unit comprises a sleeve 22 preferably of nickeland having a rare earth coating such as barium, strontium, caesium or other thermionically active material. As herein shown the unit includes also a supplementary grid comprising a loose spiral coil of tungsten or molybdenum wire 23 which is arranged concentrically and in spaced relation to the sleeve 22 comprising the cathode and is also coated with barium or the like. The grid 23 serves to save the coating and so prolong the life of the cathode. The free electrode comprises a perforated sleeve 24 of tungsten, nickel or molybdenum arranged concentrically as the outer member of the unit and fitting into a peripheral shoulder of the upper and lower flanges I 9 and IT. A small amount of mercury (Hg) is shown as present in the bulb in the form of an amalgam ball, this providing mercury vapor within the bulb.

The internal electrical circuit of the tube is diagrammatically shown in Fig. 4 from which it will appear that the heater wire 2ll-2| forms a complete circuit through the tube and that the electrode 22 and grid 23 of both units are connected to the lead wires l3 and I4 respectively. In other words, the full potential of the line is impressed between sleeve electrodes 22 of the two units. If this is an A. C. circuit the electrode 22 of one unit acts as the cathode during half the cycle while the electrode 22 of the other unit serves as an anode and vice versa in the other half of the cycle.

When the tube shown in Fig. 1 is screwed into the service socket the line potential difference, which may be 110 volts for example, becomes effective between the two electrode units tending to cause the electrons to flow to the sleeve 22 of the unit acting instantaneously as the anode and this eflect is intensified by heat from the heater wires 20. Current accordingly flows through the tube in increasing intensity as the flow of electrons increases. As this current flows certain of the electrons are intercepted and retained by the free electrode 24 and these build up and form a barrier to the flow of electrons in a manner limiting the flow of current through the tube. The retarding effect of the barrier will finally prevent any further increase in the intensity of the current flow through the tube and eventually produce a condition of equilibrium. However, when this is reached the electrons held upon the barrier will begin to be released, the effectiveness of the barrier will be reduced and the intensity of current will accordingly increase. The electron flow will consequently again increase and the retarding eifect of the barrier will again be built up. The result is a balanced condition in which the intensity of current flowing through the tube is maintained substantially constant.

So long as current flows into the tube the electrode units will be surrounded with a luminious discharge and this will fill the space between them as well as much of the space surrounding them. The reflecting coating l5 acts partially to hood the electrode units and to reflect outwardly light rays which would otherwise pass out through the conical portion of the bulb I 0. The field of illumination is therefore in general directed outwardly through the globe end of the bulb and concentrated by the addition of beams reflected from the surface I5.

The tube shown in Fig. 5 is similar to that already described except that the heater wire 40 is doubled back on itself within the body portion 38 of the core. The two vertical bends of the heater wire 40 are separated by an insulating partition 45 and the downwardly extending bends are connected at their lower ends by a wire 4|. As in the electrode unit already described the body 38 of the core is surrounded by a nickel sleeve 42 having a rare earth coating and serving either as the cathode or anode depending on whether the potential impressed thereon'is positive or negative. The sleeve 42 in turn is surrounded by a mesh grid 43 and outside this is the free electrode 44 which comprises a perforated sleeve of tungsten, nickel or molybdenum. As shown in Fig. 7 current may be assumed to flow to the unit through the lead wire 34, passing through the heater wire 40 and out by the lead wire 33. The sleeve 42 and the grid 43 in each unit are connected to their respective lead wires so that the full potential of the line is impressed between them and when the electrodes 42 and grids 43 are heated, electronic discharge takes place between them as already explained.

The tube shown in Fig. 8 has a single electrode unit divided into two sections by a sectional insulator 65. In this tube the heater wire 60 is doubled upon itself about an insulating strip 65 within the sleeve portion 58 of the core, and each end of the heater wire is directly connected to one of the lead wires 53 or 54. The heater wire 6D is yieldingly suspended by a spring 6| seated upon the surface of the end flange 48. The electrode tube 64 is split longitudinally and one half separated from the other by the partition 65. It may comprise a nickel coated sleeve and each half acts as cathode or anode depending upon the polarity of the potential impressed upon it. Semi-cylindrical mesh grid sections 63 surround the electrode 62, and the free electrode 64 which comprises separate semi-cylindrical sections of a perforated nickel sleeve surround the grid.

Current flowing from the heater wire 88 heats the tube sections of the electrode 62 and causes an electron discharge to flow from one half section to the other of the tube. The current of electrons is interrupted and controlled by the free electrode '64 in the manner already explained and while current flows the electrode unit is surrounded by a luminous discharge.

The tube shown in Fig. 12 has an electrode" unit which is divided horizontally rather than vertically. The bulb 10 is provided with a reflecting coating 15 and the electrode unit is supported upon a pair of insulating tubes 16 which surround the lead wires 13 and 14. The core of the unit comprises the lower flangel'l, the tubular body portion 18 and the top flange 19 together with an intermediate stepped flange 89. The electrodes comprise sleeves 82 and 82' of coated nickel extending between the lower flange 11 of the core and the intermediate flange 89 and thereafter extending from the intermediate flange 89 to the top flange 19. Both electrodes are surrounded by a mesh grid 83 or 83' of tubular shape. Outside the grids are located the free electrodes which comprise perforated nickel sleeves 84 and 84' insulated from each other by the intermediate flange 89. The heater wire 80 is doubled upon itself about an insulating strip 88 and the bight of the wire is yieldingly suspended by a spring 8| located above the upper flange 19. The lower electrode 82 and grid 83 are connected to the lead-in wire 14 as shown in the circuit diagram of Fig. 14. The upper electrode 82 and grid 83' are connected by the wire 86 to a terminal 85 at the upper end of the bulb and this in turn is connected to the metal piece H of an external connecting wire 81. This is but one means of bringing the upper half of the electrode into connection with the base of the bulb and any other suitable connection would be within the scope of the present invention.

The current flowing from the heater wire 88 heats both electrodes and permits an electronic current between them which carries the current from the tube and is controlled by the action of the free electrode in the manner already explained.

While the illustrated units are shown as including a coiled heater wire it will be understood that any other type of heater may be employed which is convenient or appropriate to the design of the unit.

The inner reflecting coating of the bulb may be silver deposited in any satisfactory manner as for example, by vaporizing in the partially evacuated bulb by heat supplied in a high frequency field or by resistance heating. Aluminum, nickel or alloys of these metals with silver and magnesium may be employed if desired. The metallic coating may be removed to clear portions of the bulb by acid or mechanically.

The terms free electrode and free grid used in the annexed claims are defined as an electrode and a grid which are not electrically connected to another electrode and which are not connected electrically as by a lead wire to the exterior of the tubes in which they are used.

Having thus disclosed my invention and described several embodiments thereof for purposes of illustration but not by way of limitation what I claim as new and desire to secure by Letters Patent is:-

1. In an automatically regulating electron tube containing gas, an electrode unit comprising a heater, a cylindrical cathode surrounding the same, a grid spaced outside the walls of the oathode, and a cylindrical free electrode enclosing said cathode and grid.

2. In an automatically regulating electron tube containing gas, an electrode unit comprising a refractory core enclosing a heater, a cylindrical cathode surrounding the core, a cylindrical free electrode spaced from the cathode, and a grid arranged concentrically between the cathode and the free electrode, said free electrode being arranged partially to intercept electrons traveling from the cathode and temporarily to retain electrons thereon.

3. In an automatically regulating electron tube containing gas, an electrode unit comprising a refractory core enclosing a resistance heater, a tubular cathode located in proximity to the heater and electrically connected thereto, and insulating members supporting a perforated tubular free grid around and in spaced relation to the cathode.

4. In an automatically regulating electron tube, an electrode unit comprising a refractory core containing a resistance heater, elongated segmental electrode sections mounted adjacent to the core and insulated from each other, and a cylindrical electrode enclosing said electrode sections and insulated therefrom.

5. In an automatically regulating electron tube, an electrode unit comprising a refractory core containing a resistance heater, cylindrical electrode sections threaded on the core and insulated from each other and electrically connected at spaced points to the heater, and a perforated cylindrical electrode enclosing said electrode sections and insulated therefrom.

6. An electrode unit for an electric lamp containing gas, comprising a refractory tube containing a heating coil and having end flanges, an electrode tube surrounding said refractory tube and engaging said end flanges, and a free electrode encasing the electrode tube and also engaging said flanges.

'7. In an electron tube containing gas, a heater, a thermionically active cathode around said heater, and a free grid around said cathode.

8. In an electron tube containing gas, a heater, a cathode having its outer surface coated with an alkaline earth metal around said heater, and a free grid around said cathode.

9. In a gaseous electron tube adapted for alternating current operation, a pair of heaters, a pair of spaced thermionically active electrodes one around each of said heaters and adapted to function alternatively one as a cathode while the other functions simultaneously as an anode, and a free grid around each of said electrodes.

10. An electron tube comprising a thermionically active cathode, a grid around and electrically connected to said cathode, and a free electrode around said grid.

11. An electron tube comprising a heater, a cathode around and electrically connected to said heater, a grid around and electrically connected to said cathode, and a free electrode around said rid.

12. In a gaseous electron tube adapted for alternating current operation, a pair of heaters, a pair of spaced, cylindrical, thermionically active electrodes one around each of said heaters, arranged along-side and substantially parallel to each other and adapted to function alternatively one as a cathode while the other functions as an m anode, and a free grid surrounding each of said electrodes.

13. In a gaseous electron tube adapted for alternating current operation and having a socket and an envelope symmetrically connected to said socket, a pair ,of spaced, cylindrical, thermionically active electrodes arranged along a line extending through said socket, a free grid surrounding each of said electrodes, and a common heater within said electrodes.

MICHEL E, MACKSOUD. 

